Survey of implementations: http://common-lisp.net/~dlw/LispSurvey.html
CL HyperSpec: http://www.lisp.org/HyperSpec/FrontMatter/index.html
Practical Common Lisp: http://www.gigamonkeys.com/book/
On Lisp: http://www.paulgraham.com/onlisptext.html
SICP: http://mitpress.mit.edu/sicp/ (relates to Scheme, a Lisp-1; CL is a Lisp-2)